The main objectives of this research project will be (1) to determine the pulmonary excretion rate of carbon monoxide (VECO) in very small premature infants as an index of red blood cell turnover in the postnatal period, and (2) to correlate VECO with levels of blood carboxyhemoglobin (COHb), hemoglobin, reticulocyte count, platelet count, serum tocopherol (vitamin E), and bilirubin. Carbon monoxide, which is excreted via the lungs, is produced in equimolar amounts with bilirubin during the catabolism of heme, mainly from the hemoglobin in red blood cells. It is often not possible, using conventional laboratory tests, to ascertain whether a prominent reticulocytosis during the second postnatal month in a premature infant is secondary to a recovering bone marrow after the hemoglobin concentration has reached its physiologic nadir or to an abnormal degree of hemolysis related to a low level of serum tocopherol. The determination of VECO is a sensitive, noninvasive means of defecting increases in heme catabolism as a reflection of hemolysis. This would be especially useful for monitoring the hemolytic effect of iron, a known oxidant, in premature infants, who may be deficient in the antioxidant, vitamin E. We have developed an open, flow-through hood collection system for the determination of CO excretion rates without contamination of the samples by room air. In addition, we have developed a gas chromatograph analyzer, utilizing a unique detector with a CO resolution of .33 time 10 to the minuse 12 power moles or .003 ppm (parts per million) per 2.5 ml sample. Thus, we can measure VECO with a noninvasive technique that is extremely accurate.